Fractional photon-assisted tunneling of ultra-cold atoms in periodically shaken double-well lattices

Fractional photon-assisted tunneling is investigated both numerically and analytically in a double-well lattice. While integer photon-assisted tunneling is a single-particle effect, fractional photon-assisted tunneling is an interaction-induced many-body effect. Double-well lattices with few particles in each double well are ideal to study this effect far from the mean-field effects. It is predicted that the 1/4-resonance is observable in such systems. Fractional photon-assisted tunneling provides a physically relevant model, for which N-th order time-dependent perturbation theory can be large although all previous orders are small. All predicted effects will be observable with an existing experimental setup [1]

Setting New Jersey Hospital Rates: A Regulatory System Under Stress

This Article reviews the history of hospital rate setting in New Jersey, emphasizing the system\u27s evolution in response to newly perceived problems and changing political forces. The system experienced some early success in controlling cost growth and demonstrating new techniques of hospital rate setting. In later years, rate setting in New Jersey has been less successful at confronting a new federal role and the growing problem of health care access. The problems faced by New Jersey hold lessons for both the federal government as it pursues cost containment and the other states who either operate rate regulation systems or contemplate them for the future

Disorder Induced Effects on the Critical Current Density of Iron Pnictide BaFe_1.8 Co_0.2 As_2 single crystals

Investigating the role of disorder in superconductors is an essential part of characterizing the fundamental superconducting properties as well as assessing potential applications of the material. In most cases, the information available on the defect matrix is poor, making such studies difficult, but the situation can be improved by introducing defects in a controlled way, as provided by neutron irradiation. In this work, we analyze the effects of neutron irradiation on a Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ single crystal. We mainly concentrate on the magnetic properties which were determined by magnetometry. Introducing disorder by neutron irradiation leads to significant effects on both the reversible and the irreversible magnetic properties, such as the transition temperature, the upper critical field, the anisotropy, and the critical current density. The results are discussed in detail by comparing them with the properties in the unirradiated state.Comment: accepted for Ph

Cornelius Lanczos's derivation of the usual action integral of classical electrodynamics

The usual action integral of classical electrodynamics is derived starting from Lanczos's electrodynamics -- a pure field theory in which charged particles are identified with singularities of the homogeneous Maxwell's equations interpreted as a generalization of the Cauchy-Riemann regularity conditions from complex to biquaternion functions of four complex variables. It is shown that contrary to the usual theory based on the inhomogeneous Maxwell's equations, in which charged particles are identified with the sources, there is no divergence in the self-interaction so that the mass is finite, and that the only approximation made in the derivation are the usual conditions required for the internal consistency of classical electrodynamics. Moreover, it is found that the radius of the boundary surface enclosing a singularity interpreted as an electron is on the same order as that of the hypothetical "bag" confining the quarks in a hadron, so that Lanczos's electrodynamics is engaging the reconsideration of many fundamental concepts related to the nature of elementary particles.Comment: 16 pages. Final version to be published in "Foundations of Physics

Frequency Dependent Flux Dynamics and Activation Energies in Pnictide Bulk (Ba0.56K0.44)Fe2As2 Superconductor

AbstractThermally activated flux de-pinning and flux activation de-pinning energies are studied in a (Ba0.56K0.44)Fe2As2 (Tc=38.5K) bulk superconductor in DC magnetic fields up to 18 T. Ac susceptibility was measured as a function of temperature, DC and AC magnetic fields, and frequency. Ac susceptibility curves shift to higher temperatures as the frequency is increased from 75 to 1997Hz in all fields. We model this data by Arrhenius law to determine flux activation energies as a function of AC and DC magnetic fields. The activation energy ranges from 8822K at μ0 Hdc = 0 T to 1100K at 18 T for Hac =80 A/m. The energies drop quickly in a non-linear manner as DC field rises above 0 T and around 1 T, which we describe as pinning transition field, the drop levels and continues more slowly in a linear like manner as DC field approaches to 18 T. Furthermore, the activation energy drops quickly as AC field increases from 80 A/m to 800 A/m at 0 DC field. As the DC field rises above 0, the activation energy has significantly weaker dependence on the AC field amplitude. Extensive map of the de-pinning, or irreversibility, lines shows broad dependence on the magnitude of the small AC field, frequency, in addition to the DC field

Inter- and Intra-granular flux Pinning in Ba(Fe0.91Co0.09)2As2 Superconductors

AbstractThermally assisted flux flow (TAFF) and flux pinning energiesare studied in a Ba(Fe0.91Co0.09)2As2 (Tc = 25.3K) sample via resistivity and AC susceptibility measurements in magnetic fields up to 18T. The flux pinning energy U(T,H) is determined from the Arrhenius law. The pinning maxima well determined by resistivity measurements ranged from 1724K at 0 T to 585K at 18 T with a sharp drop off so that U(T=Tc) varied with the applied field H as . The pinning activation energies determined from the AC susceptibility data but were by a factor of three higher, which is explained here. Both inter- and intra-granular pinning energies are determined in low fields. The onset of TAFF temperature and the crossover temperature Tx from TAFF to flux flow are determined, showing the limitations of the Anderson-Kim model

Detecting the Most Distant (z>7) Objects with ALMA

Detecting and studying objects at the highest redshifts, out to the end of Cosmic Reionization at z>7, is clearly a key science goal of ALMA. ALMA will in principle be able to detect objects in this redshift range both from high-J (J>7) CO transitions and emission from ionized carbon, [CII], which is one of the main cooling lines of the ISM. ALMA will even be able to resolve this emission for individual targets, which will be one of the few ways to determine dynamical masses for systems in the Epoch of Reionization. We discuss some of the current problems regarding the detection and characterization of objects at high redshifts and how ALMA will eliminate most (but not all) of them.Comment: to appear in Astrophysics and Space Science, "Science with ALMA: a new era for Astrophysics", ed. R. Bachille

Quantum state-dependent diffusion and multiplicative noise: a microscopic approach

The state-dependent diffusion, which concerns the Brownian motion of a particle in inhomogeneous media has been described phenomenologically in a number of ways. Based on a system-reservoir nonlinear coupling model we present a microscopic approach to quantum state-dependent diffusion and multiplicative noise in terms of a quantum Markovian Langevin description and an associated Fokker-Planck equation in position space in the overdamped limit. We examine the thermodynamic consistency and explore the possibility of observing a quantum current, a generic quantum effect, as a consequence of this state-dependent diffusion similar to one proposed by B\"{u}ttiker [Z. Phys. B {\bf 68}, 161 (1987)] in a classical context several years ago.Comment: To be published in Journal of Statistical Physics 28 pages, 3 figure

Thermodynamics of quantum dissipative many-body systems

We consider quantum nonlinear many-body systems with dissipation described within the Caldeira-Leggett model, i.e., by a nonlocal action in the path integral for the density matrix. Approximate classical-like formulas for thermodynamic quantities are derived for the case of many degrees of freedom, with general kinetic and dissipative quadratic forms. The underlying scheme is the pure-quantum self-consistent harmonic approximation (PQSCHA), equivalent to the variational approach by the Feynman-Jensen inequality with a suitable quadratic nonlocal trial action. A low-coupling approximation permits to get manageable PQSCHA expressions for quantum thermal averages with a classical Boltzmann factor involving an effective potential and an inner Gaussian average that describes the fluctuations originating from the interplay of quanticity and dissipation. The application of the PQSCHA to a quantum phi4-chain with Drude-like dissipation shows nontrivial effects of dissipation, depending upon its strength and bandwidth.Comment: ReVTeX, 12 pages, 9 embedded figures (vers.2: typo mistake fixed

Cosmological Tracking Solutions

A substantial fraction of the energy density of the universe may consist of quintessence in the form of a slowly-rolling scalar field. Since the energy density of the scalar field generally decreases more slowly than the matter energy density, it appears that the ratio of the two densities must be set to a special, infinitesimal value in the early universe in order to have the two densities nearly coincide today. Recently, we introduced the notion of tracker fields to avoid this initial conditions problem. In the paper, we address the following questions: What is the general condition to have tracker fields? What is the relation between the matter energy density and the equation-of-state of the universe imposed by tracker solutions? And, can tracker solutions explain why quintessence is becoming important today rather than during the early universe